1. Field
The embodiment relates to a power supply circuit, a power supply control circuit, and a power supply control method.
2. Description of the Related Art
Recently, a memory card has become wide-spread as a data recording medium of portable electronic equipment (digital camera, mobile phone, etc.). The operation voltage of a memory card is determined in accordance with the operation voltage of a non-volatile memory (flash memory etc.) mounted on the memory card. For example, there exist a non-volatile memory with the operation voltage of 3.3 V and one with that of 1.8 V. Consequently, there also exist a memory card with the operation voltage of 3.3 V and one with that of 1.8 V.
In order to make the operation voltage of a memory card independent from that of an internal non-volatile memory, it is required to mount a DC-DC converter on the memory card. It is necessary for the memory card to mount, in addition to a non-volatile memory, a logic circuit for controlling the non-volatile memory. However, it is inefficient to mount two kinds of logic circuits (a logic circuit for 3.3 V and that for 1.8 V) on a memory card in accordance with the operation voltage of the non-volatile memory and when the fact that the voltage of a semiconductor device constituting a logic circuit is fixed accompanying the reduction in size thereof is considered, it is desirable to mount only the logic circuit for 1.8 V on the memory card. However, it is required to mount both the DC-DC converter for the logic circuit and that for the non-volatile memory on the memory card. By the way, techniques relating to a DC-DC converter are disclosed in Japanese Unexamined Patent Application Publication No. Hei 7-21791, Japanese Unexamined Patent Application Publication No. Hei 9-154275, Japanese Unexamined Patent Application Publication No. Hei 9-294368, etc.
It is possible to realize the independence of the operation voltage of the memory card from that of the internal non-volatile memory by mounting a DC-DC converter on the memory, however, it is very inefficient only to mount simply two or more DC-DC converters on the memory card. In addition, since the memory card is inserted/removed into/from electronic equipment in an activated state, when a voltage required inside the memory card is generated by a boost DC-DC converter, there arises a problem that the input voltage flows through to the output side when the memory card is inserted into the electronic equipment, causing an inrush current. Further, if the rising timing of the power supply voltage of the non-volatile memory and the power supply voltage of the logic circuit is not considered, there is the possibility of the risk of burn-out caused by latch-up of the semiconductor device constituting the non-volatile memory or the logic circuit.